In the drilling of bore holes or wells into or through earth formation, it has become a much used practice to drive the drill bit by an in-hole fluid driven motor, such as a turbine or positive displacement or progressive cavity motor having a stator through which fluid flows from a running in string of drill pipe or fluid conduit, driving the motor rotor which is connected with the bit.
It is customary to provide a valve between the motor and the conduit or pipe string which is normally open when the assembly is lowered in the well bore and when the assembly is pulled from the well bore, so that the conduit for pipe string above the motor can fill with fluid or be drained of fluid.
Such valves are generally constructed to be responsive to the circulation of drilling fluid down the conduit or pipe string to close the opening or passage between the pipe string and the annulus, so that all of the drilling fluid is caused to flow to the motor. An example of such a valve is that disclosed in U.S. Pat. No. 3,005,507, granted Oct. 24, 1961, to E. H. Clark, Jr., et al, for Fluid By-Pass For Rotary Drill Bits.
From time to time, it becomes desirable or necessary to circulate drilling fluid with the drill bit off the bottom of the hole, say to flush drilling fluid and cuttings from the hole for a period of time or while rotating the runnng pipe string to release it or prevent it from becoming stuck, or to free a stuck bit. With the usual fill or dump valve, as described above, circulation of drilling fluid without weight on the bit requires that the fluid flow through the motor, causing undesired wear on the motor and bearings, or alternatively that a separate circulation sub be employed in the pipe string. Such a circulation sub is shown, by way of example, in U.S. Pat. No. 3,989,114, granted Nov. 2, 1976, to me and John E. Tschirky, entitled Circulation Sub For In-Hole Hydraulic Motors. The circulation sub of that patent is well suited for its intended purposes, but requires that a blanking plug or mandrel be removably disposed in the shiftable valve member to open the valve and enable the circulation, as well as subsequent retrieval of the mandrel by a wire line tool.